Gas analysis apparatus



Feb. 26, 1952 F. F. YANlKosKl GAS ANALYSIS APPARATUS F1ed 00b. 18, 1946IMI Patented Feb. 26, 1952 UNITED PATENT OFFICE assasse Qns .finntxslsAPPARATUS` Florian Yanilkxoski, ChiagQ Hight Aphlicaation Qctgber 18,1956, Serial No. 703.980

i clavier. (o1. ca -2s) (Granted `under the act of March 3, 1883, as

amended April 3Q, 192g: 370'0. G. "757) The invention described hereinmay -be manufactured and used by or for the Government `for governmentalpurposes Without paymentt me of any royalty thereon.` f

This invention relates to gas analysis apparaf tus of the type thatcontinuously 'determines the percentage of one gas in a mixture of twoor more gases. One object of the invention'is to provide a gas analysisapparatus capableof Avery high speeds in responding to a change in thecorniposition of the sample. Another object is to provide an apparatusof simple construction which provides accurate analyses substantiallyindependent of the temperature and pressure of the surroundingatmosphere. Still vvanother object is to provide an apparatus capable of safely analyzing explosive mixtures of gases. Still -another object isto provide a gas analysis apparatus which utilizes the fact that therelaitive viscosities of gases change as a function 'of temperature.Still another object is to provide an apparatus which utilizes thefact'thatth viscosity of gas apparently changes when the width of theflow path is reducedy to values approaching that of the mean freemoleculair path.

These and other objects will be vapparent to those skilled in the artfrom theiollowing'description and the related drawings. 'i

In the drawings:

Fig. 1 is a sectional view of the preferred form ofthe invention shownconnected to one type of pressure differential indicator;

Fig. 2 is an exploded view of some o f the parts shown in Fig. 1;

Fig. 3 is an enlarged sectional viewof the orif fice plate;

"Fig 4 is a sectional vieW of an alternate type of heat exchanger;

Fig. 5 is a sectional view of an alternate Ytype of restriction to flow;

Fig. 6 is a sectional View of another alternate type of heat exchanger;and

Fig. 7 is a sectional view of another alternate type of restriction.

Similar reference numerals indicate the saine parts throughout theseveral views. v

My invention is embodied in various combinaf tions of apparatus whichcause a samplff g'aslto undergo pressure changes depending .0X1 tliechemical n-ature of the sample,` Yand indicating or recording apparatusoperatedbythe saidiprsfsure change. When considering a"m`ix'tu`re""oftwo definite gases the pressure-operated'I ratus may be calibrated`directlyin terirs percentage of each gas present in.`.th `e.s

More specically, the measured pressure drop occurs as th'e'sample passesthrough restrictions which cause viscous drag,` the volumetric oWrateth'rough the said restrictions being determinedV by causing thesample' gas to pass through an orifice at the maximum rate. The maximumrate of 'flow for some gases is considerably'diiferent from that ofother gases, but is substantially independent of the pressure upstreamof the oricev provided the absolute pressure downstream of oriice doesnot exceed approximately'one-half the absolute' pressure upstream of theoriiice. Since the viscosity of gases is also substantially independentof the pressure, the viscous pressure 'drop' developed in therestriction is substantially independent of the pressure'of the sample.

-` Both the viscosity and the maximum ow rate of all gases are functionsVof temperature, therefore preferable combinations of apparatus includemeans to correct the temperature of the sample to within a fraction of adegree of a predetermined temperature before the sample passes throughthe restriction and the orifice; Assuming a'constant temperature,4 thepressure drop developed by viscous ow through the restricis' (l) C, G1,C2, Cs-constants A-"orilice' area; ft2. g`gravtational const. IL-degreesRankine.` R-gas constant. lc-ratio of'spec.' heats. ruf-#molecularweight.

4 VS/Triting Ras :154/molecularweight and combining all constants, (.2.)becomes Substituting the value of lo into Equation .1, and combiningconstants The long radical in Equation 4 may be replaced by approximatevalues tabulated below:

For inert gases (helium and argon) .725

For diatomic gases (N2, O2, air, CO, HC1,

NO, etc.) .685

For complex gases (hydrocarbons, etc.)-

varies .64 to .67

Values of pressure drop relative to air are listed below for certaincommon gases:

Pressure drop relative to .air for a certain analyzer operating at 100F.

While this list is far from complete, it serves to illustrate the widedifference in pressure drops developed in some cases. The pressure dropfor each of the gases listed above is sufciently different from othersthat mixtures of any two could be analyzed. A complete table of gaseswould lead to innumerable other combinations that could be analyzed.Certain groups of gases, such as CO, N2, and air, have substantiallyidentical pressure drops and may be treated in any proportions as asingle gas when analyzing for one other gas, such as CO2, which has asubstantially different pressure drop.

Since viscosity is a function of temperature, the relative values wouldbe somewhat different if the operating temperature of the analyzer werechanged. By choosing the proper temperature it is possible in some casesto cause two or more gases t undergo an identical pressure drop, andunder these circumstances any proportions of said gases may be treatedas a single gas when analyzing for still another gas. When seeking sucha temperature it is only necessary to plot curves of pressure dropagainst temperature for the various gases concerned and choose thetemperature at which the pressure curves cross or become tangent.

The pressure drop developed by viscous flow through a resistance is, inaddition to the temperature, also a function of the mean free path ofthe gas molecules provided the cross section of the flow path is notlarge compared to the length of the molecular free path. By meansdescribed later in this discussion, the average cross section of the owpath may be reduced to the point where the relative pressure drops maybe changed slightly to cause two or more gases to have an identicalpressure drop for the purpose of determining the percentage of stillanother gas having a substantially different pressure drop. Furthermore,by combining the effect of changing the operating temperature and theeffect of changing the cross section of the flow path, still othergroups of gases may be caused to develop identical pressure drops forthe purpose of analyzing for one gas in a mixture of more than twogases.

The means used to accomplish the operations described above arecombinations of apparatus which will now be described.

The preferred embodiment of my invention is illustrated in Fig. 1. Athermostatic control of any type known to the art. but in this instancee tuations in temperature.

represented by a thermostatic switch I and heater winding 2 operates tomaintain all the internal parts at substantially a certain constanttemperature.

Any suitable insulation 3 minimizes heat exchange between the ambientair and the internal parts of the analyzer. A main body 4, hereafterknown as the heat reservoir, provides a heat capacity sufficiently largeto prevent sudden fluc- A further function of the heat reservoir is toconduct heat to all the internal parts. Still another function of theheat reservoir is to provide a convenient body to which other parts aresecured.

An inlet fitting 5-insulates the internal parts from externallyconnected parts such as a filter, drier, saturator, chemical absorber orother preparatory apparatus well known in the art while conducting thegas sample from the said preparatory apparatus to a heat exchanger 6.The heat exchanger, preferably formed of porous metal, but which canalternatively be formed of porous ceramic, glass or other material,efficiently heats the gas passing through its numerous channels. A heatexchanger so constructed is highly preferred to others because of itsability to change the temperature of a sample as much as 200 F. in afraction of a second and yield a terminal temperature within a fractionof a degree of the desired temperature. Accuracy combined with speed intemperature control provides response not obtainable with heatexchangers commonly used. The retainer 'I, made of any heat conductingmaterial, has a preferably tapered hole into which the porous materialis fitted. An alternate type of heat exchanger illustrated in Fig. 4,consists of individual pieces of material 8 packed into a retainer 9 andheld in place by end plugs I0 and II which have passages to pass gas butto retain solids. The material 8 may be beads, chips, strands, or othersmall shapes of any material, but preferably good heat conductors. Stillanother heat exchanger which may be used but which is not preferred isillustrated in Fig. 6. This heat exchanger 29 consists of any heatconducting material through which is formed one or more holes to conductthe sample. Gasket I2 serves as a pressure seal and as a means ofexerting force on the threads of parts 4 and 'I to insure efficient heattransfer.

A restriction I3 to flow is made of porous mal terial having numerousflow paths of small cross section. For many purposes porous metal issuperior, but alternately porous ceramic, glass or other materials maybe used. A retainer I4 held tightly against a gasket I5 by a spring I6,preferably fits freely in the heat reservoir 4 so that it may be easilyinterchanged with other retainers. Such construction permits quickchanges in the operating characteristics of the analyzer if retainerscontaining various types of restrictive material are made available. Inaddition to the type of restriction made of molded porous materials,other restrictions shown in Fig. 5 and Fig. 7 may be used. Therestriction in Fig. 5 is structurally similar to that of the heatexchanger in Fig. 4, consisting of particles of material 24, retainer25, and end plugs 2B and 2l. The restriction 28 shown in Fig. 7represents many possible arrangements of one or more capillary channels,but in this case consists of a metal plug through which holes of smalldiameter are formed.

Fittings I 'I and I8 provide means to connect any suitable device formeasuring pressure drops developed in the restriction I3. A manometer I9is representative of numerous indicators, re-

corders, or controllers known to the art which operate on a pressuredifferential. For example, a diaphragm operated by the diierentialpressure at ttings I1 and I8 could control valves in such a manner thatthe analyzer apparatus tends to maintain a mixture of definiteproportions downstream of the said valves.

An orice 20 in an orifice plate 2l passes a volume of gas substantiallyindependent of the pressure of the gas provided the absolute pressuredownstream of the orice does not exceed approximately one-half theabsolute pressure upstream of the orifice. An outlet tting 22 serves asa mounting for the orice plate, as a thermal insulator, and as a meansto connect to any suitable evacuating pump (not shown). No evacuatingpump is required if the gas sample enters the analyzer at a pressurehigh enough above atmospheric pressure to satisfy the conditions forcritical ow. A gasket 23 prevents leakage of gas around the threads oftting 22.

It is understood that the details of construction are not necessarilylimited to those described above in the preferred embodiment of myinvention.l The invention consists in certain improvements andcombinations of parts set forth in the following claim.

What I claim as my invention:

A gas analysis apparatus comprising an insulated heat reservoir throughwhich is formed a passage for the ow of gas to be analyzed, a heaterwinding adjacent to the said heat reservoir, a thermostatic switchoperating in a manner to close and open a circuit including the saidheater winding. an elongated porous mass heat exchanger removablymounted in the said gas passage, a retainer for the said heat exchangerremovably mounted in the said passage, an elongated porous restrictionremovably mounted in the said gas passage, a retainer for the saidelongated restriction removably mounted in the said passage, insulatingfittings mounted in the said heat reservoir in such a manner that theirinternal openings connect to the said passage at opposite ends of thesaid elongated porous restric tion, an insulating gas connector at theoutlet end of the said passage, and a restrictive orifice plate mountedin the said connector between the orice plate and outlet, and means tomaintain on opposite sides of the said orice plate a pressure dropsufficient to cause maximum flow.

FLORIAN F. YANIKOSKI.

' REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,272,059 Lacey July 9, 19181,633,352 Tate June 21, 1927 1,884,896 Smith Oct. 25, 1932 2,154,862Olshevsky Apr. 18, 1939 2,163,730 Goetzl June 27, 1939 FOREIGN PATENTSNumber Country Date 435,176 Great Britain Dec. 8, 1933 OTHER REFERENCESPhysics Text Book- Hausmann and Slack (Van Nostrand) published September1935.

